Resin for photoresist composition, photoresist composition and method for forming resist pattern

ABSTRACT

A resin for photoresist compositions is disclosed with excellent resolution and line edge roughness characteristics. A photoresist composition and a method for forming a resist pattern using such a resin are also disclosed. The resin has a hydroxyl group bonded to a carbon atom at a polymer terminal, and the carbon atom in the α-position to the hydroxyl group has at least one electron attractive group.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/557,694, filed Nov. 22, 2005, which is the US National Phase filingunder 35 U.S.C. § 371 of PCT/JP2004/008004, filed on Jun. 2, 2004, whichclaims priority under 35 U.S.C. § 119(a)-(d) to Japanese PatentApplication No. 2003-160478, filed Jun. 5, 2003; Japanese PatentApplication No. 2003-428853, filed Dec. 25, 2003; and Japanese PatentApplication No. 2004-57449, filed Mar. 2, 2004. The contents of theseapplications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a resin for a photoresist composition,a photoresist composition, and a method for forming a photoresistcomposition.

BACKGROUND ART

Until recently, polyhydroxystyrenes or derivatives thereof in which thehydroxyl groups are protected with acid dissociable, dissolutioninhibiting groups, which display high transparency relative to a KrFexcimer laser (248 nm), have been used as the base resin component ofchemically amplified resists. However, these days, the miniaturizationof semiconductor elements has progressed even further, and thedevelopment of processes that use ArF excimer lasers (193 nm) to producevery fine resist patterns of 130 nm or less is being vigorously pursued.

For processes using an ArF excimer laser as the light source, resinssuch as polyhydroxystyrenes that contain benzene rings have insufficienttransparency relative to the ArF excimer laser (193 nm).

Accordingly, resins capable of resolving this problem, which contain nobenzene rings and exhibit superior levels of transparency and dryetching resistance, and which include, within the principal chain, astructural unit derived from a (meth)acrylate ester that includes apolycyclic hydrocarbon ring such as an adamantane skeleton at the estergrouping have already been proposed (see patent references 1 through 8).

Examples of this type of conventional photoresist composition includechemically amplified compositions containing a resin component obtained,for example, by radical polymerization, an acid generator component, andan organic solvent. Furthermore, in the patent reference 9, a resin isdisclosed in which polymerization is conducted using a chain transferagent that contains no polar groups at the terminals.

(Patent Reference 1) Japanese Patent (Granted) Publication No. 2,881,969

(Patent Reference 2)

Japanese Unexamined Patent Application, First Publication No. Hei5-346668

(Patent Reference 3)

Japanese Unexamined Patent Application, First Publication No. Hei7-234511

(Patent Reference 4)

Japanese Unexamined Patent Application, First Publication No. Hei9-73173

(Patent Reference 5)

Japanese Unexamined Patent Application, First Publication No. Hei9-90637

(Patent Reference 6)

Japanese Unexamined Patent Application, First Publication No. Hei10-161313

(Patent Reference 7)

Japanese Unexamined Patent Application, First Publication No. Hei10-319595

(Patent Reference 8)

Japanese Unexamined Patent Application, First Publication No. Hei11-12326

(Patent Reference 9)

Japanese Unexamined Patent Application, First Publication No. 2001-2735

In recent years, the design rules required in semiconductor elementproduction have continued to become more stringent, and improvements inresolution, such as a resolution of no more than 130 nm, and in thevicinity of 100 nm, are now being required. In addition, the occurrenceof line edge roughness (LER) in the resist pattern following developingis also a problem. This LER appears as distortions around the holepatterns in a hole resist pattern, or as non-uniform irregularities inthe side walls in a line and space pattern. As demands for higherresolutions grow, this LER must continue to be reduced. Furthermore, assemiconductor elements undergo ever greater miniaturization, reductionsin the level of defects are also keenly sought.

However, the improvements in LER and defect occurrence provided byconventional photoresist compositions are inadequate.

DISCLOSURE OF INVENTION

The present invention takes the above circumstances into consideration,with an object of providing a resin that can be used in a photoresistcomposition which exhibits favorable resolution and LER characteristics,and enables a reduction in the level of defects, as well as providing aphotoresist composition and a method for forming a resist pattern thatuse such a resin.

In the present invention, the above object was achieved by the followingaspects.

Namely, a first aspect of the present invention provides a resin for aphotoresist composition, wherein the resin has a hydroxyl group bondedto a carbon atom at a polymer terminal, and the carbon atom in theα-position to the hydroxyl group has at least one electron attractivegroup.

A second aspect of the present invention is a resin for a photoresistcomposition, having a substituent with a pKa value of 6 to 12 at apolymer terminal.

A third aspect of the present invention is a photoresist compositionthat includes a resin for a photoresist composition according to thepresent invention.

A fourth aspect of the present invention is a method for forming aresist pattern that uses a photoresist composition of the presentinvention.

In this description, the term “structural unit” refers to a monomer unitwhich contributes to the formation of a polymer (resin).

EFFECTS OF THE INVENTION

The present invention is able to provide a photoresist composition and amethod for forming a resist pattern that exhibit improved resolution andLER characteristics, and a reduced level of defects.

BEST MODE FOR CARRYING OUT THE INVENTION Resin for Resist Composition

First Aspect

A resin for a resist composition according to the first aspect has ahydroxyl group bonded to a carbon atom at a polymer terminal, and thecarbon atom in the α-position to the hydroxyl group has at least oneelectron attractive group.

Examples of this electron attractive group include a halogen atom or ahalogenated alkyl group or the like.

Examples of suitable halogen atoms include a fluorine atom, a chlorineatom, or the like, although a fluorine atom is preferred.

In a halogenated alkyl group, the halogen refers to the same halogenatoms as described above. The alkyl group is preferably a lower alkylgroup of 1 to 3 carbon atoms, and is preferably a methyl group or ethylgroup, and most preferably a methyl group. Specific examples of suitablegroups include a trifluoromethyl group, difluoromethyl group,monofluoromethyl group, and perfluoroethyl group, although atrifluoromethyl group is particularly desirable.

The number of electron attractive groups is either 1 or 2, but ispreferably 2.

The above description of a resin having a hydroxyl group bonded to acarbon atom, wherein the carbon atom in the α-position to the hydroxylgroup has at least one electron attractive group can be expressed morespecifically, and ideally, as a resin having a —CR¹R²OH group, whereinR¹ and R² each represent, independently, an alkyl group, halogen atom,or halogenated alkyl group, and at least one of R¹ and R² is an electronattractive group selected from the group consisting of halogen atoms andhalogenated alkyl groups.

The halogen atoms and halogenated alkyl groups are as defined above,whereas suitable examples of the alkyl group include lower alkyl groupssuch as a methyl group, ethyl group, or propyl group. The lower alkylgroup preferably contains from 1 to 5 carbon atoms. As described above,the electron attractive group is preferably a fluorine atom or afluorinated alkyl group, and compounds in which both R¹ and R² arefluorinated alkyl groups, and particularly trifluoromethyl groups, arepreferred in terms of the ease of synthesis, and the effect of thecompound in reducing LER.

In this resin for a photoresist composition, the proportion ofstructural units (M1) that include the aforementioned —CR¹R²OH groupbonded to a polymer terminal (hereafter, this group may also be referredto as the “terminal structure”) is preferably at least 1 mol % (andpreferably 2 mol % or higher) relative to the combined 100 mol % of allthe structural units other than the structural units (M1) within thephotoresist composition resin (resin for a photoresist composition).

This combination of all the structural units other than the structuralunits (M1) includes structural units derived from a conventionalpolymerization initiator such as azobisisobutyronitrile (AIBN), andstructural units derived from the monomer that represents the primarycomponent of the resin.

There are no particular restrictions on the upper limit for the aboveproportion, although considering practical factors such as theproduction method, the value is typically no more than 5 mol %.Furthermore, depending on the nature of the composition, if theproportion of the above terminal structures is too high, thenundesirable phenomena such as thickness loss in the resist pattern, andslight tapering at the base of the patterns may occur. The number ofmols of the structural unit (M1) is, of course, equal to the number ofmols of the terminal structure, and the number of mols of hydroxylgroups.

By ensuring that the proportion is at least 1 mol %, a superior LERimprovement effect can be realized as a result of the introduction ofthe terminal structure. If the proportion is less than 1 mol %, thenthere is a tendency for this effect to deteriorate.

The terminal structure can be introduced at a polymer terminal, forexample, by adding a chain transfer agent containing a —CR¹R²OH groupduring production of the polymer by radical polymerization using amonomer and a polymerization initiator. In this case, the structuralunit (M1) containing the terminal structure is a structural unit (M1)derived from the chain transfer agent.

The chain transfer agent is represented, for example, by a generalformula X—R′—CR¹R²OH.

In this formula, X represents a hydroxyl group or thiol group, and thistype of chain transfer agent bonds to the polymer terminal throughelimination of the hydrogen atom of the hydroxyl group or thiol group.Accordingly, the structural unit (M1) in this case is the unit generatedwhen the hydrogen atom is removed from the hydroxyl group or thiol groupof the group X within the formula X—R′—CR¹R²OH. In terms of reactivity,X is most preferably a thiol group.

Furthermore, R′ represents a bivalent aliphatic hydrocarbon group (whichmay be a straight-chain, branched-chain, or cyclic group) or a bivalentaromatic hydrocarbon group, and of these, a straight-chain orbranched-chain aliphatic hydrocarbon group is preferred.

An example of a suitable alicyclic group is a cyclohexylene group. Anexample of a suitable aromatic hydrocarbon group is a p-phenylene group.

Examples of suitable straight-chain and branched-chain aliphatichydrocarbon groups include a methylene group, ethylene group,n-propylene group, and isopropylene group, and of these, an ethylenegroup or n-propylene group is preferred.

Preferred chain transfer agents can be represented by the generalformula SH—(CH₂)_(m)—C(CF₃)₂—OH (wherein, m represents an integer from 2to 4). Accordingly, preferred forms for the structural unit (M1) can berepresented by a general formula —S—(CH₂)_(m)—C(CF₃)₂—OH.

The proportion of the terminal structure (the proportion of thestructural unit (M1)) can be altered by adjusting the relativequantities of the monomer and the chain transfer agent, and by adjustingthe timing of the addition of the chain transfer agent, thereby alteringthe weight average molecular weight of the resin for the resistcomposition.

Furthermore, in a synthesized resist composition resin, the number ofmols of the terminal structure (the number of mols of the structuralunit (M1)) can be measured by NMR techniques (nuclear magnetic resonancespectroscopy) such as proton-NMR or carbon-NMR.

There are no particular restrictions on the structural units other thanthe structural unit (M1), and any units typically used in resins forresist compositions, and preferably units that are produced by radicalpolymerization, can be used.

The present invention can be applied to resins for either non-chemicallyamplified or chemically amplified photoresist compositions, althoughchemically amplified compositions are preferred.

Furthermore, the present invention can be applied to either negative orpositive chemically amplified compositions, although positivecompositions are preferred. Examples of resins for chemically amplifiedpositive resist compositions include resins in which acid dissociable,dissolution inhibiting groups (protective group) have been introducedinto a hydroxystyrene-based resin, which are widely used with KrFexcimer lasers, and resins in which acid dissociable, dissolutioninhibiting groups have been introduced into a (meth)acrylate-based resin(wherein the term (meth)acrylate refers to acrylate and/ormethacrylate), which are widely used with ArF excimer lasers.

As the acid dissociable, dissolution inhibiting group, any of the groupsused with hydroxystyrene-based resins and (meth)acrylate-based resinscan be used.

Specific examples of suitable groups include chain-like alkoxyalkylgroups, tertiary alkyloxycarbonyl groups, tertiary alkyl groups,tertiary alkoxycarbonylalkyl groups, and cyclic ether groups.

Examples of suitable chain-like alkoxyalkyl groups include 1-ethoxyethylgroups, 1-methoxymethylethyl groups, 1-isopropoxyethyl groups,1-methoxypropyl groups, and 1-n-butoxyethyl groups; examples of suitabletertiary alkyloxycarbonyl groups include tert-butyloxycarbonyl groupsand tert-amyloxycarbonyl groups; examples of suitable tertiary alkylgroups include chain-like tertiary alkyl groups such as tert-butylgroups and tert-amyl groups, and tertiary alkyl groups that contain analiphatic polycyclic group, such as 2-methyl-2-adamntyl groups and2-ethyl-2-adamantyl groups; examples of suitable tertiaryalkoxycarbonylalkyl groups include tert-butyloxycarbonylmethyl groupsand tert-amyloxycarbonylmethyl groups; and examples of suitable cyclicether groups include tetrahydropyranyl groups and tetrahydrofuranylgroups. As follows is a description of specific examples of preferred(meth)acrylate-based resins of the present invention.

Examples of the structural units other than the structural unit (M1)include the following types of units.

(a1): Structural units derived from a (meth)acrylate ester containing anacid dissociable, dissolution inhibiting group.

The resin may also contain the structural units (a2) and (a3) describedbelow, and resins that contain the structural units (a1) and (a2) arepreferred, and resins that contain (a1), (a2), and (a3) are even moredesirable.

(a2): Structural units derived from a (meth)acrylate ester containing alactone ring.(a3): Structural units derived from a (meth)acrylate ester containing ahydroxyl group.

Normally, in addition to the aforementioned terminal structure, a smallquantity of structural units derived from the radical polymerizationinitiator are also introduced at the polymer terminals.

Structural Unit (a1)

In the structural unit (a1), there are no particular restrictions on theacid dissociable, dissolution inhibiting group. Typically, groups thatform cyclic or chain-like tertiary alkyl esters with the side-chaincarboxyl group of a (meth)acrylate are widely known, and of these,aliphatic monocyclic or polycyclic group-containing acid dissociable,dissolution inhibiting groups are preferred, and aliphatic polycyclicgroup-containing acid dissociable, dissolution inhibiting groups areparticularly desirable.

Examples of aliphatic monocyclic groups include groups in which onehydrogen atom has been removed from a cycloalkane. Specific examplesinclude groups in which one hydrogen atom has been removed from acyclohexane or the like.

Examples of aliphatic polycyclic groups include groups in which onehydrogen atom has been removed from a bicycloalkane, tricycloalkane ortetracycloalkane or the like. Specific examples include groups in whichone hydrogen atom has been removed from a polycycloalkane such asadamantane, norbornane, isobornane, tricyclodecane ortetracyclododecane. Of these groups, adamantyl groups, norbornyl groups,and tetracyclododecanyl groups are preferred industrially.

More specific examples include the groups represented by the generalformulas (I), (II), and (III) shown below.

(wherein, R represents a hydrogen atom or a methyl group, and R¹represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R² and R³each represent, independently, a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁴represents a tertiary alkyl group)

In the formulas, the group R¹ is preferably a lower straight-chain orbranched alkyl group of 1 to 5 carbon atoms, and suitable examplesinclude a methyl group, ethyl group, propyl group, isopropyl group,n-butyl group, isobutyl group, pentyl group, isopentyl group, andneopentyl group. Of these, a methyl group or ethyl group is preferred interms of industrial availability.

The aforementioned groups R² and R³ each preferably represent,independently, a lower alkyl group of 1 to 5 carbon atoms. Of thestructural units represented by the formula (II), cases in which R² andR³ are both methyl groups are preferred industrially, and specificexamples include structural units derived from 2-(1-adamantyl)-2-propyl(meth)acrylate.

The aforementioned group R⁴ is a tertiary alkyl group such as atert-butyl group or tert-amyl group, although structural units in whichR⁴ is a tert-butyl group are preferred industrially.

Furthermore, the group —COOR⁴ may be bonded to either position 3 or 4 ofthe tetracyclododecanyl group shown in the formula, and the bondingposition cannot be further specified. Similarly, the carboxyl groupresidue of the (meth)acrylate structural unit may be bonded at eitherposition 8 or 9 in the formula, and the bonding position cannot befurther specified.

The structural unit (a1) typically accounts for 20 to 60 mol %, andpreferably from 30 to 50 mol %, of the combined total of all thestructural units.

Structural Unit (a2)

Examples of the structural unit (a2) include structural units in whicheither a monocyclic group formed from a lactone ring, or an aliphaticpolycyclic ring containing a lactone ring, is bonded to an ester sidechain of a (meth)acrylate ester. Here, the term lactone ring refers to asingle ring that contains a —O—C(O)— structure, and this ring is countedas the first ring. Accordingly, the case in which the only ringstructure is the lactone ring is referred to as a monocyclic group, andgroups containing other ring structures are described as polycyclicgroups regardless of the structure of the other rings.

Specific examples of the structural unit (a2) include monocyclic groupsin which one hydrogen atom has been removed from γ-butyrolactone, andpolycyclic groups in which one hydrogen atom has been removed from alactone group-containing bicycloalkane.

Specifically, structural units represented by structural formulas (IV)to (VII) shown below are preferred.

(wherein, R represents a hydrogen atom or a methyl group, and mrepresents either 0 or 1)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

The structural unit represented by the formula (VI) exists as anisomeric mixture in which the bonding position of the (meth)acrylategroup to the polycyclic group is a mixture of position 5 and position 6.

(wherein, R represents a hydrogen atom or a methyl group)

The structural unit (a2) typically accounts for 20 to 60 mol %, andpreferably from 30 to 50 mol %, of the combined total of all thestructural units.

Structural Unit (a3)

As the structural unit (a3), any of the multitude of structural unitsproposed for inclusion within resins for photoresist compositions foruse with ArF excimer lasers and the like can be used, and hydroxylgroup-containing aliphatic polycyclic groups are preferred. Thepolycyclic group can be selected appropriately from the same pluralityof polycyclic groups described above in relation to the aforementionedstructural unit (a1).

Specifically, as the structural unit (a3), units that include a hydroxylgroup-containing adamantyl group or a carboxyl group-containingtetracyclododecanyl group can be used particularly favorably.

Even more specific examples include structural units represented by ageneral formula (VIII) shown below.

(wherein, R represents a hydrogen atom or a methyl group)

The structural unit (a3) typically accounts for 10 to 50 mol %, andpreferably from 10 to 40 mol %, of the combined total of all thestructural units.

Furthermore, other structural units (a4) different from the structuralunits (a1) to (a3) can also be included.

There are no particular restrictions on the structural unit (a4),provided it is a different structural unit that cannot be classified asany of the above structural units (a1) through (a3).

For example, structural units containing an aliphatic polycyclic groupand derived from a (meth)acrylate ester are preferred. Suitable examplesof the polycyclic group include similar groups to those listed in theabove description for the structural unit (a1), and one or more groupsselected from amongst tricyclodecanyl groups, adamantyl groups, andtetracyclododecanyl groups is preferred in terms of industrialavailability.

Specific examples of the structural unit (a4) include the structuresshown below in formulas (IX) to (XI).

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

The structural unit (a4) typically accounts for 1 to 25 mol %, andpreferably from 5 to 20 mol %, of the combined total of all thestructural units.

The resist composition resin may include a single resin, or a mixture oftwo or more different resins.

A resin for a resist composition of the present invention can beobtained by polymerizing the monomers that give rise to the structuralunits other than the structural unit (M1), for example by a conventionalradical polymerization using a radical polymerization initiator such asazobisisobutyronitrile, and then adding a chain transfer agentcontaining the aforementioned terminal group, thereby causing chaintransfer in the polymerization, at a time that is most suitable in termsof regulating the weight average molecular weight and adjusting theproportion of the structural unit (M1) within the resin.

The weight average molecular weight (the polystyrene-equivalent weightaverage molecular weight determined by gel permeation chromatography,this also applies to all subsequently molecular weight values) of theresist composition resin of the present invention is typically no morethan approximately 12,000, and preferably no more than 10,000, and evenmore preferably 8,000 or less.

By restricting the molecular weight to 8,000 or less, the quantity ofthe terminal group introduced into the resin can be increased, therebyenhancing the LER improvement effect. Furthermore, another effect isachieved in that a more rectangular pattern cross-sectional shape can beobtained.

Although there are no particular restrictions on the lower limit for themolecular weight, in terms of suppressing pattern collapse and improvingthe resolution, a value of at least 4,000 is preferred, and values of5,000 or greater are even more desirable.

In the first aspect, by employing this type of structure for the resistcomposition resin, the LER characteristics can be improved. In addition,the occurrence of resist pattern collapse can also be suppressed.Furthermore, this reduction in pattern collapse improves the resolution.Furthermore, the depth of focus characteristics also improve, and thelevel of defects also decreases.

The reason for the improvement in LER is not entirely clear, although itis surmised that whereas the polymer terminals of conventional resincomponents obtained by radical polymerization include structures derivedfrom hydrophobic polymerization initiators or hydrophobic chain transferagents (terminators), which may inhibit the solubility of the resin inthe alkali developing solution, in the present invention, the existenceof the electron attractive group means the hydrogen atom of the hydroxylgroup can readily dissociate, thereby imparting a suitable degree ofacidity to the resin, and consequently improving the solubility of theresin in the alkali developing solution, and improving the LERcharacteristics at the interface between the exposed portions and theunexposed portions of the resist pattern.

Second Aspect

A resin for a resist composition according to the second aspect has asubstituent with a pKa value of 6 to 12, and preferably from 7 to 10, ata polymer terminal.

By ensuring a pKa value within this range, a suitable degree of aciditycan be generated, meaning favorable LER characteristics can be achieved,and enabling swelling of the resist pattern to be suppressed.

An example of a group capable of generating a hydrogen ion at the abovesubstituent group is an alcoholic hydroxyl group.

The hydroxyl groups of carboxyl groups tend to have pKa values that aretoo small, meaning an undesirable degree of swelling occurs upon alkalideveloping.

The pKa of the substituent group is small if an electron attractivegroup is bonded to the carbon atom in the α-position to the alcoholichydroxyl group, and is large if no such electron attractive groupexists. In other words, the pKa value varies depending on thecharacteristics of the terminal structure, which includes the abovealcoholic hydroxyl group, the carbon atom in the α-position, and theatoms and/or substituent groups bonded to this α-carbon atom (butexcluding the carbon atom at the β-position).

The pKa can be altered by adjusting the nature and number of electronattractive groups bonded to the carbon atom at the α-position, and byadjusting the nature of substituent groups at the polymer terminal.

In other words, by bonding an electron attractive group to the carbonatom at the α-position, in a similar manner to the first aspect, the pKavalue can be reduced.

In order to satisfy the above pKa numerical range, a configuration ofthe first aspect is preferred, and a structure in which the substituentis a —CR¹R²OH group (wherein, R¹ and R² each represent, independently,an alkyl group, halogen atom, or halogenated alkyl group, and at leastone of R¹ and R² is an electron attractive group selected from the groupconsisting of halogen atoms and halogenated alkyl groups) isparticularly desirable.

The pKa value is represented by the acid dissociation constant in anaqueous solution. The pKa value can be measured by preparing a monomerfor which the degree of acidity of the terminal structure can bemeasured, and then measuring the pKa using a quantitative method such astitration.

Furthermore, the pKa value can also use values reported in referencedocuments and the like.

In the second aspect, by using a resist composition resin with this typeof structure, the LER characteristics can be improved.

In addition, the occurrence of resist pattern collapse can also bereduced. Furthermore, this reduction in pattern collapse improves theresolution. Furthermore, the depth of focus characteristics alsoimprove. The level of defects also decreases.

The reason for the improvement in LER is the same as the reasondescribed for the first aspect.

[Photoresist Composition]

Provided a photoresist composition of the present invention uses a resinfor a resist composition according to the present invention, there areno particular restrictions on the other components within thecomposition.

For example, in the case of a chemically amplified positive photoresistcomposition, the composition includes a resin component (A), which is aresist composition resin according to the present invention that alsocontains acid dissociable, dissolution inhibiting groups, an acidgenerator component (B), an organic solvent (C), and where necessary,other components such as a nitrogen-containing organic compound (D) orthe like. Hereafter is a description of a sample composition that issuited to exposure using an ArF excimer laser.

The quantity of the component (A) may be adjusted in accordance with thefilm thickness of the resist being formed. Typically, the quantity ofthe component (A), reported as a solid fraction concentration, is withina range from 8 to 25% by weight, and is preferably from 10 to 20% byweight.

Acid Generator Component (B)

In the present invention, the component (B) may include known acidgenerators used in conventional chemically amplified photoresistcompositions. A large variety of acid generators are already known,including onium salts such as iodonium salts and sulfonium salts, oximesulfonates, bisalkyl or bisaryl sulfonyl diazomethanes, nitrobenzylsulfonates, iminosulfonates, and disulfones, and any of these known acidgenerators can be used without any particular restrictions.

Of these, (b-0) onium salts that include a fluorinated alkylsulfonateion as the anion result in the generation of stronger acids, and areconsequently ideal.

Examples of suitable cations for these (b-0) onium salts include mono-or diphenyliodonium cations, and mono-, di-, or triphenyl sulfoniumcations, all of which may be substituted with lower alkyl groups such asmethyl groups, ethyl groups, propyl groups, n-butyl groups, andtert-butyl groups, or lower alkoxy groups such as methoxy groups andethoxy groups; as well as dimethyl(4-hydroxynaphthyl)sulfonium cationsor the like.

Furthermore, the anion for the onium salt (b-0) is preferably afluorinated alkylsulfonate ion.

Of these, a fluorinated alkylsulfonate ion in which either a portion of,or all of, the hydrogen atoms of a straight-chain alkyl group of 1 to 7carbon atoms, and preferably 1 to 3 carbon atoms, have been fluorinatedis particularly desirable. Ensuring the number of carbon atoms is nomore than 7 increases the strength of the resulting sulfonic acid.

Furthermore, the fluorination ratio (the proportion of fluorine atomswithin the alkyl group) of the fluorinated alkylsulfonate ion ispreferably within a range from 10 to 100%, and even more preferably from50 to 100%, and anions in which all of the hydrogen atoms have beensubstituted with fluorine atoms are particularly desirable as they yieldstronger acids.

Specific examples of this type of anion include thetrifluoromethanesulfonate, heptafluoropropanesulfonate, andnonafluorobutanesulfonate anions.

Specific examples of (b-0) include diphenyliodoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, bis(4-tert-butylphenyl)iodoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, (4-methoxyphenyl)phenyliodoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, tri(4-methylphenyl) sulfoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, (4-methylphenyl)diphenylsulfoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, dimethyl(4-hydroxynaphthyl)trifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, monophenyldimethylsulfoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, diphenylmonomethylsulfoniumtrifluoromethanesulfonate, heptafluoropropanesulfonate ornonafluorobutanesulfonate, triphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate,tri(p-tert-butylphenyl)sulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate, and(4-trifluoromethylphenyl)diphenylsulfonium trifluoromethanesulfonate,heptafluoropropanesulfonate or nonafluorobutanesulfonate.

In the present invention, iminosulfonate-based acid generators, whichrepresent a different acid generator from the aforementioned (b-0)salts, can also be used favorably.

Specific examples of suitable iminosulfonate-based acid generatorsinclude compounds represented by general formulas (b-1) and (b-2) shownbelow (hereafter, these compounds may also be referred to as sulfoniumcompounds 1 and sulfonium compounds 2 respectively).

In the general formulas (b-1) and (b-2), X represents a straight-chainor branched alkylene group in which at least one hydrogen atom has beensubstituted with a fluorine atom, and the number of carbon atoms withinthe alkylene group is typically within a range from 2 to 6, andpreferably from 3 to 5, and most preferably 3.

Y and Z each represent, independently, a straight-chain or branchedalkyl group in which at least one hydrogen atom has been substitutedwith a fluorine atom, and the number of carbon atoms within the alkylgroup is typically within a range from 1 to 10, and preferably from 1 to7, and most preferably from 1 to 3. Lower numbers of carbon atoms withinthe alkylene group X or the alkyl groups Y and Z result in bettersolubility within the resist solvent, which is desirable.

Furthermore, in the alkylene group X or the alkyl groups Y and Z, thelarger the number of hydrogen atoms that have been substituted withfluorine atoms, the stronger the acid becomes, and the transparencyrelative to high energy light beams of 200 nm or less or electron beamsalso improves favorably. The fluorine atom proportion within thealkylene group or alkyl groups, namely the fluorination ratio, ispreferably within a range from 70 to 100%, and even more preferably from90 to 100%, and perfluoroalkylene or perfluoroalkyl groups in which allof the hydrogen atoms have been substituted with fluorine atoms are themost desirable.

R¹ to R³ each represent, independently, an aryl group or an alkyl group.

Of the groups R¹ to R³, at least one group is an aryl group. Compoundsin which at least two of R¹ to R³ represent aryl groups are preferred,and compounds in which all of R¹ to R³ are aryl groups are the mostpreferred.

There are no particular restrictions on the aryl groups of R¹ to R³, andsuitable examples include aryl groups of 6 to 20 carbon atoms, such asphenyl groups and naphthyl groups, which may, or may not, be substitutedwith alkyl groups and/or halogen atoms and the like. In terms ofenabling low cost synthesis, aryl groups of 6 to 10 carbon atoms arepreferred.

There are no particular restrictions on the alkyl groups of R¹ to R³,and suitable examples include straight-chain, branched, or cyclic alkylgroups of 1 to 10 carbon atoms. From the viewpoint of achievingexcellent resolution, alkyl groups of 1 to 5 carbon atoms are preferred.Specific examples include a methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, n-pentyl group,cyclopentyl group, hexyl group, cyclohexyl group, nonyl group, anddecanyl group, although in terms of achieving superior resolution andenabling low cost synthesis, a methyl group is the most desirable.

Of the above possibilities, compounds in which R¹ to R³ are all phenylgroups are the most preferred.

The compounds represented by these general formulas (b-1) and (b-2) canbe used either alone, or in combinations of two or more differentcompounds. Of the possible compounds, sulfonium compounds 1 representedby the general formula (b-1) are preferred, and the compound representedby a chemical formula (XIII) shown below is the most preferred.

In the present invention, by combining at least one compound selectedfrom the above sulfonium compounds 1 and 2, with an aforementioned resinfor a resist composition according to the present invention, aparticularly superior defect reduction effect is achieved. Here, theterm “defect” refers to scum and general resist pattern abnormalitiesdetected by inspection of a resist pattern following developing, fromdirectly above the resist pattern, using a surface defect inspectiondevice (brand name: KLA) from KLA Tencor Corporation. These types ofdefects can cause reductions in process yields, and a deterioration inthe product performance, and consequently represent an extremely largeproblem. A number of factors are thought to cause these defects,including the resist resolution performance, irregularities in thealkali solubility arising from insoluble matter or impurities within theresist, and the surface state of the resist.

The reason for the above defect reduction effect is thought to relate tothe fact that, as described above, the resist resolution performance isone cause of defects, and it is believed that the resolution has asignificant effect on the level of defects. It is thought that becausethe sulfonium compounds 1 and 2 include a bulky iminosulfonate structureas shown in the formulas (b-1) and (b-2), the diffusion length is shorteven if the number of carbon atoms is small, and consequently, a highlevel of resolution results. Particularly in the case of the sulfoniumcompounds 1, the presence of the cyclic structure means the diffusionlength is even shorter, thereby suggesting an even higher resolution canbe expected. It is thought that this results in a reduction in the levelof defects.

This type of defect reduction effect is particularly important in thosecases where a fine contact hole (CH) pattern is to be formed. This isbecause when a fine CH pattern is formed, patterning must be conductedwith a very low light intensity to ensure formation of a CH pattern ofvery small size, and this leads to an increase in the likelihood ofdefects such as blockages within the upper or interior portions of theCH pattern, or color irregularities.

In those cases where a mixture of an aforementioned (b-0) salt and atleast one compound selected from amongst the sulfonium compounds 1 and 2is used as the above (B) component, the proportion of the (b-0) salt ispreferably within a range from 10 to 75% by weight, and even morepreferably from 30 to 70% by weight. By using a blend of the (b-0) saltthat falls within the above range, a resin with particularly superiorLER and defect (developing defect) characteristics can be obtained.

Furthermore, the blend ratio (weight ratio) between the (b-0) salt andthe one or more compounds selected from amongst the sulfonium compounds1 and 2 is preferably within a range from 1:9 to 9:1, and preferablyfrom 1:5 to 5:1, and even more preferably from 1:2 to 2:1. By mixing theacid generators using this type of ratio, a resin with particularlysuperior LER and developing defect characteristics can be obtained.Using a mixture of a sulfonium compound represented by the generalformula (b-1) and a (b-0) salt is the most preferred configuration.

The component (B) is preferably used in a quantity within a range from0.1 to 30 parts by weight, and preferably from 0.5 to 20 parts byweight, and even more preferably from 1 to 10 parts by weight, per 100parts by weight of the component (A). At quantities below the lowerlimit of the above range, image formation becomes impossible, whereas ifthe quantity exceeds 30 parts by weight, forming a homogeneous solutionbecomes difficult, and there is a danger of a deterioration in storagestability.

Organic Solvent (C)

A positive resist composition of the present invention can be producedby dissolving the above materials in an organic solvent (C) (hereafterreferred to as the component (C)).

As the component (C), any solvent capable of dissolving the componentsused to generate a homogeneous solution is suitable, and the solventused can be one, or two or more solvents selected from amongst knownsolvents used for conventional chemically amplified resists.

Examples of suitable solvents include γ-butyrolactone, ketones such asacetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone and2-heptanone; polyhydric alcohols and derivatives thereof such asethylene glycol, ethylene glycol monoacetate, diethylene glycol,diethylene glycol monoacetate, propylene glycol, propylene glycolmonoacetate, dipropylene glycol, or the monomethyl ether, monoethylether, monopropyl ether, monobutyl ether or monophenyl ether ofdipropylene glycol monoacetate; cyclic ethers such as dioxane; andesters such as methyl lactate, ethyl lactate, methyl acetate, ethylacetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, and ethyl ethoxypropionate. Mixed solvents ofpropylene glycol monomethyl ether acetate (PGMEA) and a polar solventare preferred. The mixing ratio within this type of mixed solvent can bedetermined on the basis of the co-solubility of the PGMEA and the polarsolvent, but is preferably within a range from 1:9 to 8:2, and even morepreferably from 2:8 to 5:5

More specifically, in those cases where ethyl lactate (EL) is added asthe polar solvent, the weight ratio of PGMEA:EL is preferably within arange from 2:8 to 5:5, and even more preferably from 3:7 to 4:6.Furthermore, as the organic solvent, a mixed solvent of at least one ofPGMEA and EL, together with γ-butyrolactone is also preferred. In suchcases, the weight ratio between the former and latter components ispreferably within a range from 70:30 to 95:5. There are no particularrestrictions on the quantity used of the component (C), which is set inaccordance with the resist film thickness so as to produce aconcentration that enables favorable application of the composition to asubstrate, and is typically sufficient to produce a solid fractionconcentration within the resist composition of 2 to 20% by weight, andpreferably from 5 to 15% by weight.

Nitrogen-Containing Organic Compound (D)

In order to improve the resist pattern shape and the post exposurestability of the latent image formed by the pattern-wise exposure of theresist layer, a nitrogen-containing compound (D) can also be added as anoptional component (D).

A multitude of these nitrogen-containing organic compounds have alreadybeen proposed, and one of these known compounds can be used, although anamine, and particularly a secondary lower aliphatic amine or tertiarylower aliphatic amine is preferred.

Here, a lower aliphatic amine refers to an alkyl or alkyl alcohol amineof no more than 5 carbon atoms, and examples of these secondary andtertiary amines include trimethylamine, diethylamine, triethylamine,di-n-propylamine, tri-n-propylamine, triisopropylamine, tripentylamine,diethanolamine, triethanolamine, and triisopropanolamine, and tertiaryalkanolamines such as triethanolamine are particularly preferred. Thesemay be used either alone, or in combinations of two or more differentcompounds.

These compounds are typically added in a quantity within a range from0.01 to 5.0 parts by weight per 100 parts by weight of the component(A).

Furthermore, in order to prevent any deterioration in sensitivity causedby the addition of the aforementioned component (D), and improve theresist pattern shape and the post exposure stability of the latent imageformed by the pattern-wise exposure of the resist layer, an organiccarboxylic acid, or a phosphorus oxo acid or derivative thereof can alsobe added as an optional component (E). Either one, or both of thecomponent (D) and the component (E) can be used.

Examples of suitable organic carboxylic acids include malonic acid,citric acid, malic acid, succinic acid, benzoic acid, and salicylicacid. Of these, salicylic acid is preferred.

Examples of suitable phosphorus oxo acids or derivatives thereof includephosphoric acid or derivatives thereof such as esters, includingphosphoric acid, di-n-butyl phosphate and diphenyl phosphate; phosphonicacid or derivatives thereof such as esters, including phosphonic acid,dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid,diphenyl phosphonate and dibenzyl phosphonate; and phosphinic acid orderivatives thereof such as esters, including phosphinic acid andphenylphosphinic acid, and of these, phosphonic acid is particularlypreferred.

The component (E) is typically used in a quantity within a range from0.01 to 5.0 parts by weight per 100 parts by weight of the component(A).

Other Optional Components

Other miscible additives can also be added to a photoresist compositionaccording to the present invention according to need, and examplesinclude additive resins for improving the properties of the resist film,surfactants for improving the ease of application, dissolutioninhibitors, plasticizers, stabilizers, colorants and halation preventionagents.

[Method for Forming Resist Pattern]

There are no particular restrictions on the method for forming a resistpattern according to the present invention, provided the method uses aphotoresist composition of the present invention.

A method for forming a resist pattern of the present invention can beconducted, for example, in the manner described below.

Namely, a positive photoresist composition of the present invention isfirst applied to the surface of a substrate such as a silicon waferusing a spinner or the like, a prebake is conducted under temperatureconditions of 80 to 150° C. for 40 to 120 seconds, and preferably for 60to 90 seconds, and then following selective exposure of an ArF excimerlaser through a desired mask pattern using, for example, an ArF exposureapparatus, PEB (post exposure baking) is conducted under temperatureconditions of 80 to 150° C. for 40 to 120 seconds, and preferably for 60to 90 seconds. Subsequently, developing is conducted using an alkalideveloping solution such as a 0.1 to 10% by weight aqueous solution oftetramethylammonium hydroxide. In this manner, a resist pattern which isfaithful to the mask pattern can be obtained.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied layer of the resist composition.

Furthermore, there are no particular restrictions on the wavelength usedfor the exposure, and depending on the characteristics of the resistcomposition resin, an ArF excimer laser, KrF excimer laser, F₂ excimerlaser, or other radiation such as EUV (extreme ultraviolet), VUV (vacuumultraviolet), electron beam, X-ray or soft X-ray radiation can be used.

In this manner, in the present invention, a resist resin with favorableLER characteristics can be provided, and consequently, a photoresistcomposition can be provided that is ideal for the production ofsemiconductor elements and liquid crystal elements and the like. Byappropriate selection of the structural units of the resist resin, achemically amplified photoresist composition can be provided that isparticularly suitable for use with wavelengths of 200 nm or shorter, andparticularly ArF excimer lasers.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples.

Example 1

0.1 mols of a monomer containing a 50/30/20 (mol %) mixture ofγ-butyrolactone methacrylate (the monomer that corresponds with the unitof the general formula (VII) wherein R is a methyl group),2-methyl-2-adamantyl methacrylate (the monomer that corresponds with theunit of the general formula (I) wherein R is a methyl group and R¹ is amethyl group), and 3-hydroxy-1-adamantyl acrylate (the monomer thatcorresponds with the unit of the general formula (VIII) wherein R is ahydrogen atom) was dissolved in 150 ml of THF (tetrahydrofuran), aradical polymerization was initiated at 70° C. using AIBN (in a quantityequivalent to 4 mol % relative to 100 mol % of the above monomer), thecompound represented by a chemical formula (XIV) shown below (pKa valueof the terminal structure: approximately 7) was added as apolymerization chain transfer agent, in a quantity equivalent to 2 mol %relative to 100 mol % of the combination of the above monomer and AIBN,and a polymerization reaction was conducted.

Following completion of the polymerization reaction, the reactionsolution was poured into 2,000 ml of n-heptane, the resulting mixturewas stirred for 30 minutes at 25° C., and the precipitated solid wasrecovered by filtration. This solid was then redissolved in 200 ml ofTHF, and once again poured into 2,000 ml of n-heptane, stirred for 30minutes at 25° C., and the resulting precipitated resin was recovered byfiltration. The weight average molecular weight of the resin was 10,000.

To 100 parts by weight of the thus obtained resist composition resin(the component (A)) were added and dissolved the components listedbelow, thus producing a positive photoresist composition.

Component (B): 3.0 parts by weight of triphenylsulfoniumnonafluorobutanesulfonate

Component (D): 0.1 parts by weight of triethanolamine.

Component (C): 900 parts by weight of a mixed solvent of propyleneglycol monomethyl ether acetate and ethyl lactate (weight ratio: 80/20).

Subsequently, the thus obtained chemically amplified positivephotoresist composition was applied to the surface of a silicon waferusing a spinner, and was then prebaked (PAB treatment) and dried for 90seconds at 120° C. on a hotplate, thereby forming a resist layer with afilm thickness of 250 nm.

This film was then selectively irradiated with an ArF excimer laser (193nm) through a mask pattern, using an ArF exposure apparatus (NSR-S302,manufactured by Nikon Corporation, NA (numerical aperture)=0.60, ⅔annular illumination).

The film was then subjected to PEB treatment at 120° C. for 90 seconds,subsequently subjected to puddle development for 60 seconds at 23° C. ina 2.38% by weight aqueous solution of tetramethylammonium hydroxide, andwas then washed for 20 seconds with water, and dried.

A resist pattern formed using the exposure dose required for faithfullyreproducing a 120 nm line and space pattern (1:1) was inspected forcross-sectional shape using a SEM (scanning electron microscope).

The pattern shape was rectangular, no thickness loss was observed, andthe resolution was also favorable.

Furthermore, the depth of focus for the 120 nm line and space pattern(1:1) was 500 nm.

Furthermore, when the 3σ value, which is a measure of the line edgeroughness of the line and space pattern, was determined, the result was7.2 nm.

The 3σ value is determined by measuring the resist pattern width of thesample at 32 positions using a measuring SEM (S-9220, a brand name,manufactured by Hitachi, Ltd.), and calculating the value of 3 times thestandard deviation (3σ) from these measurement results. The smaller this3σ value is, the lower the level of roughness, indicating a resistpattern with a uniform width.

Defects were measured using a surface defect inspection device KLA2132(brand name) from KLA Tencor Corporation, and the number of defectswithin the wafer was evaluated. Three wafers were tested, and theaverage value was determined. The result revealed 3 defects.

Furthermore, when the exposure time for the selective exposure wasgradually increased, thereby making the pattern gradually finer, and ameasurement was made as to when pattern collapse occurred, it was foundthat pattern collapse occurred at a pattern width of 57 nm.

Example 2

With the exception of altering the proportion of the chain transferagent represented by the above chemical formula (XIV) from 2 mol % to 3mol %, a resist composition resin with a weight average molecular weightof 10,000 was obtained in the same manner as the example 1.

This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1

Example 3

With the exception of altering the conditions so that the weight averagemolecular weight of the resist composition resin was 7,000, a resistcomposition resin was obtained in the same manner as the example 2.

This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1.

Example 4

With the exception of altering the monomer composition to a 50/30/20(mol %) mixture of norbornanelactone acrylate (the monomer thatcorresponds with the unit of the general formula (V) wherein R is ahydrogen atom), 2-ethyl-2-adamantyl methacrylate (the monomer thatcorresponds with the unit of the general formula (I) wherein R is amethyl group and R¹ is an ethyl group), and 3-hydroxy-1-adamantylacrylate (the monomer that corresponds with the unit of the generalformula (VIII) wherein R is a hydrogen atom), a resist composition resinwith a weight average molecular weight of 7,000 was obtained in the samemanner as the example 3.

This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1.

Example 5

With the exception of altering the monomer composition to a 40/40/20(mol %) mixture of norbornanelactone methacrylate (the monomer thatcorresponds with the unit of the general formula (VI) wherein R is amethyl group), 2-ethyl-2-adamantyl methacrylate (the monomer thatcorresponds with the unit of the general formula (I) wherein R is amethyl group and R¹ is an ethyl group), and 3-hydroxy-1-adamantylmethacrylate (the monomer that corresponds with the unit of the generalformula (VIII) wherein R is a methyl group), a resist composition resinwith a weight average molecular weight of 6,400 was obtained in the samemanner as the example 1.

This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1.

Example 6

With the exception of altering the conditions so that the weight averagemolecular weight of the resist composition resin was 4,800, a resistcomposition resin was obtained in the same manner as the example 1.

This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1.

Example 7

With the exception of using 1.5 parts by weight of triphenylsulfoniumnonafluorobutanesulfonate and 1.5 parts by weight of the compoundrepresented by a chemical formula (XV) shown below as the component (B),evaluation was conducted in the same manner as the example 5. Theresults are summarized in Table 1.

Example 8

With the exceptions of altering the monomer composition to a 40/40/20(mol %) mixture of γ-butyrolactone acrylate (the monomer thatcorresponds with the unit of the general formula (VII) wherein R is ahydrogen atom), 2-methyl-2-adamantyl methacrylate (the monomer thatcorresponds with the unit of the general formula (I) wherein R is amethyl group and R¹ is a methyl group), and 3-hydroxy-1-adamantylacrylate (the monomer that corresponds with the unit of the generalformula (VIII) wherein R is a hydrogen atom), and altering theproportion of the chain transfer agent represented by the above chemicalformula (XIV) to 3 mol %, a resist composition resin with a weightaverage molecular weight of 7,000 was obtained in the same manner as theexample 1. This resin was then evaluated in the same manner as theexample 1. The results are summarized in Table 1.

Example 9

With the exceptions of altering the monomer composition to a 40/40/15/5(mol %) mixture of γ-butyrolactone methacrylate (the monomer thatcorresponds with the unit of the general formula (VII) wherein R is amethyl group), 2-methyl-2-adamantyl methacrylate (the monomer thatcorresponds with the unit of the general formula (I) wherein R is amethyl group and R¹ is a methyl group), 3-hydroxy-1-adamantylmethacrylate (the monomer that corresponds with the unit of the generalformula (VIII) wherein R is a methyl group), and tricyclodecanylmethacrylate (the monomer that corresponds with the structural unit ofthe general formula (IX) wherein R is a methyl group), and altering theproportion of the chain transfer agent represented by the above chemicalformula XIV to 3 mol %, a resist composition resin with a weight averagemolecular weight of 7,000 was obtained in the same manner as the example1 This resin was then evaluated in the same manner as the example 1. Theresults are summarized in Table 1

Comparative Example 1

With the exception of not using the chain transfer agent, the samemethod as the example 1 was used to produce a resist composition resin,and subsequently, a resist composition was then prepared with the samecomposition as that described in the example 1, and a positivephotoresist composition was prepared using the same method as theexample 1

Evaluation was then conducted in the same manner as the example 1. Theresults are summarized in Table 1

Comparative Example 2

With the exception of not using the chain transfer agent, the samemethod as the example 4 was used to produce a resist composition resin,and subsequently, a resist composition was then prepared with the samecomposition as that described in the example 1, and a positivephotoresist composition was prepared using the same method as theexample 1. Evaluation was then conducted in the same manner as theexample 1. The results are summarized in Table 1

Comparative Example 3

With the exception of not using the chain transfer agent, the samemethod as the example 5 was used to produce a resist composition resin,and subsequently, a resist composition was then prepared with the samecomposition as that described in the example 1, and a positivephotoresist composition was prepared using the same method as theexample 1. Evaluation was then conducted in the same manner as theexample 1. The results are summarized in Table 1.

TABLE 1 DOF LER Collapse Defects (nm) Shape (nm) (nm) (number) Example 1500 Rectangular 7.2 57 3 Example 2 550 Rectangular (slight 6.5 55 2 basebroadening) Example 3 500 Rectangular 5.1 58 1 Example 4 500 Rectangular6 60 1 Example 5 500 Very rectangular 5.5 55 1 Example 6 500 Rectangular6.1 60 1 Example 7 500 Very rectangular 5 55 1 Example 8 500 Rectangular7 62 1 Example 9 400 Very rectangular 6.5 55 1 Comparative 500Rectangular 9.8 72 10 example 1 Comparative 550 Rectangular 8 69 12example 2 Comparative 500 Rectangular (slight 8 65 15 example 3 basebroadening)

From the results in Table 1 it is evident that in the examples accordingto the present invention, the pattern shape is rectangular, the depth offocus characteristics are excellent, the LER characteristics arefavorable, and because the occurrence of pattern collapse has been ableto be prevented, and thus the resolution is favorable, and the level ofdefects is favorable. In the example 7, extremely favorable results wereobtained for the resist pattern shape, the LER characteristics, and thelevel of defects.

Example 10

With the exceptions of altering the monomer composition to a 40/40/20(mol %) mixture of γ-butyrolactone acrylate (the monomer thatcorresponds with the unit of the general formula (VII) wherein R is ahydrogen atom), 2-ethyl-2-adamantyl methacrylate (the monomer thatcorresponds with the unit of the general formula (I) wherein R is amethyl group and R¹ is an ethyl group), and 3-hydroxy-1-adamantylmethacrylate (the monomer that corresponds with the unit of the generalformula (VIII) wherein R is a methyl group), and altering the proportionof the chain transfer agent represented by the above chemical formulaXIV to 2.5 mol %, a resist composition resin with a weight averagemolecular weight of 7,000 was obtained in the same manner as the example1.

To 100 parts by weight of the thus obtained resist composition resinwere added and dissolved the components listed below, thus producing apositive photoresist composition.

Component (B): 2.5 parts by weight of the compound represented by theabove chemical formula (XV), and 1.0 parts by weight of the compoundrepresented by a chemical formula (XVI) shown below.

Component (D): triethanolamine (0.1 parts by weight).

Component (E): salicylic acid (0.1 parts by weight).

Component (C): a mixed solvent (1200 parts by weight) of propyleneglycol monomethyl ether acetate and ethyl lactate (weight ratio: 60/40).

Subsequently, the thus obtained positive photoresist composition wasapplied to the surface of a silicon wafer using a spinner, and was thenprebaked (PAB treatment) and dried for 90 seconds at 90° C. on ahotplate, thereby forming a resist layer with a film thickness of 220nm.

This film was then selectively irradiated with an ArF excimer laser (193nm) through a mask pattern, using an ArF exposure apparatus (NSR-S306,manufactured by Nikon Corporation, NA (numerical aperture)=0.78, σ=0.3).

The film was then subjected to PEB treatment at 90° C. for 90 seconds,subsequently subjected to puddle development for 60 seconds at 23° C. ina 2.38% by weight aqueous solution of tetramethylammonium hydroxide, andwas then washed for 20 seconds with water, and dried, thereby yielding acontact hole (CH) pattern) with a hole diameter of 300 nm and a pitch of500 nm. The sensitivity (Eop) was 18.5 mJ/cm².

Furthermore, when the level of defects was evaluated by using a surfacedefect inspection device KLA2132 (brand name) from KLA TencorCorporation to measure the number of defects within the wafer, theresult was 8.9 defects/cm². In this example, because the formed patternwas a CH pattern, the area of resist remaining on the substrate islarger than was the case for the line and space patterns (1:1) formed inthe examples 1 through 9 and the comparative examples 1 through 3. As aresult, the number of defects per wafer was somewhat higher. Because themeasurement of developing defects for very fine hole patterns isextremely difficult, developing defects were measured using a 300 nmhole pattern.

Next, the mask was changed to enable evaluation of the resolution anddepth of focus, and an isolated hole pattern (pitch: 1,000 nm) with ahole diameter of 130 nm, and a hole pattern (pitch: 220 nm) with a holediameter of 130 nm were obtained. The depth of focus values were 0.25 μmand 0.3 μm respectively.

INDUSTRIAL APPLICABILITY

The present invention provides a photoresist composition and a methodfor forming a resist pattern that offer improved resolution and LERcharacteristics, and reduced levels of defects, and is consequentlyextremely useful industrially.

1. A resin for a photoresist composition, comprising: a —CR¹R²OH groupwhich is introduced at a terminal of a principal chain of the resin; anda structural unit derived from a (meth)acrylate ester containing an aciddissociable, dissolution inhibiting group, wherein R¹ and R² eachrepresent, independently, an alkyl group, a halogen atom, or ahalogenated alkyl group, and at least one of R¹ and R² is an electronattractive group selected from the group consisting of halogen atoms andhalogenated alkyl groups.
 2. The resin for a photoresist compositionaccording to claim 1, wherein a —S—(CH₂)_(m)—C(CF₃)₂—OH group isintroduced at a terminal of a principal chain of the resin, wherein mrepresents an integer from 2 to
 4. 3. A resin for a photoresistcomposition, comprising a —S—(CH₂)_(m)—C(CF₃)₂—OH group which isintroduced at a terminal of a principal chain of the resin by adding achain transfer agent containing a —CR¹R²OH group, wherein m representsan integer from 2 to
 4. 4. The resin for a photoresist compositionaccording to claim 3, wherein said —S—(CH₂)_(m)—C(CF₃)₂—OH group isintroduced only at a terminal of a principal chain of the resin.
 5. Aphotoresist composition, comprising a resin for a photoresistcomposition according to claim 1 or
 3. 6. A photoresist compositionaccording to claim 5, further comprising an acid generator component(B).
 7. A photoresist composition according to claim 6, wherein thecomponent (B) comprises (b-0) an onium salt that comprises a fluorinatedalkylsulfonate ion as an anion.
 8. A photoresist composition accordingto claim 6, wherein the component (B) comprises a sulfonium compoundrepresented by either of general formulas (b-1) and (b-2) shown below:

wherein, X represents an alkylene group of 2 to 6 carbon atoms in whichat least one hydrogen atom has been substituted with a fluorine atom; Yand Z each represent, independently, an alkyl group of 1 to 10 carbonatoms in which at least one hydrogen atom has been substituted with afluorine atom; R¹ to R³ each represent, independently, an aryl group oran alkyl group, and at least one of R¹ to R³ is an aryl group.
 9. Aphotoresist composition according to claim 8, wherein said component (B)further comprises (b-0) an onium salt that comprises a fluorinatedalkylsulfonate ion as an anion.
 10. A photoresist composition accordingto claim 5, further comprising a nitrogen-containing organic compound.11. A method for forming a resist pattern, comprising: applying thephotoresist composition according to claim 5 to a surface of asubstrate; performing selective exposure through a desired mask pattern;and performing developing to form a resist pattern.